Spin-on filters are commonly used to separate contaminants from fluid. Spin-on filters typically mount on a mounting adaptor of a fluid circuit and receive and return fluid therefrom. Spin-on filters typically include a steel canister housing a filter element, having a closed end and an open end. At the open end, various means have been used to provide a sealed connection to the mounting adaptor. The connection requires a flow path for contaminated fluid into the canister and a flow path for filtered fluid out of the canister. Threaded baseplates have commonly been used for the connection with outer gaskets providing a sealed connection.
Current applications in hydraulics frequently use high strength filters which are adapted for use in high pressure applications. These high strength filters are used in the hydraulic systems of heavy machinery for use in industries such as agriculture or construction, for example, a hydraulic circuit for a backhoe which powers the shovel motion. In such applications the filter must be capable of withstanding pressure spikes without bursting and continuous pressure surges for sustained periods without fatigue and leakage. Because of the high pressure requirements, it is often desirable to incorporate an aluminum die cast baseplate into the filter. However, as will be discussed, aluminum die cast baseplate filters have had difficulties providing for a retaining groove while at the same sufficiently fastening the baseplate to the canister.
Insofar as reliability and user convenience are concerned, an important element in spin-on filters is an outer gasket which will remain in position on the filter until locked in sealing relationship with the mounting adaptor of a hydraulic circuit. Outer gaskets prevent fluid leakage between the mounting adaptor and the filter. Outer gaskets are commonly positioned in outer gasket grooves formed at the connection end of a filter. One way of forming a groove has been to draw the sheet steel of a stamped steel seaming lid to form a generally U-shaped channel as shown in U.S. Pat. No. 5,490,930. Seaming lids provide an intermediate mechanism for fastening the baseplate to the canister. In filters not using seaming lids, a common approach to forming the groove has been to draw a portion of the sheet steel from the canister to form a channel. Another common approach has been to form a groove into the baseplate directly.
Outer gasket grooves commonly include retaining means for aligning and securing the outer gasket in the groove during installation of the filter. The retaining means also prevents the gasket from falling out of the groove during the handling and transportation of the filter. Heretofore, aluminum baseplate filters and other steel baseplate filters have had less than acceptable approaches for providing retaining means. One common approach of providing a retaining means has been to further draw the sheet steel of either the canister or a seaming lid to form a reverse draft or a lip as shown in Misgen et al., U.S. Pat. No. 4,834,885. This approach is undesirable for many reasons, primarily because further manufacture and undue drawing of steel is necessary.
U.S. Pat. No. 4,743,347 to Stifelman, shows a different approach for providing retaining means that is used for die-cast aluminum baseplates. As shown in Stifelman, vertical ribs are die cast into the inner wall of the groove. The vertical ribs extend in a straight vertical fashion from the base of the groove to the top of the groove. The vertical ribs have forcibly pinched the outer gasket against the outer wall of the groove.
The vertical rib approach has several drawbacks. One drawback is that the task of inserting and removing the outer gasket into a vertically ribbed groove is difficult because the outer gasket must be forced in and out of the groove. The vertical rib approach also has manufacturing difficulties. One difficulty is that small casting tolerances have been necessary for the groove, the vertical ribs and the baseplate. These small tolerances have been necessary to achieve proper pinching of the gasket. A small tolerance is also necessary for the outer gasket. These small tolerances undesirably increase the precision necessary in manufacturing the filter.
Other problems exist with the vertical rib approach. The pinching of the outer gasket may cause problems when the filter is operating in a hydraulic circuit. Pinching of the outer gasket with spaced vertical ribs may make the gasket uneven which can potentially cause leakage, particularly if the small tolerances needed for the groove and gasket are not met. This problem may be amplified because the metal of the baseplate and the flexible material of the gasket comprise different materials and expand from heat at different rates.
A further feature common to spin-on type filters is that the baseplate is fastened to the canister to prevent leakage and bursting. The fastening technique also transfers torque from the canister to the baseplate to allow filter installation and removal. A common way of fastening a baseplate to the canister has been to use a stamped sheet steel seaming lid as an intermediate fastening mechanism. Other past designs have fastened the baseplate to the canister without a seaming lid. Some of these designs have provided for aluminum die cast baseplates. U.S. Pat. Nos. 5,080,787, 4,743,374 and 4,834,885 generally disclose beading or wrapping the a portion of the open end of a canister over a preformed shoulder in the baseplate.
However, both types of filters, the filters with and without seaming lids, have had disadvantages. More specifically, it has been difficult to sufficiently fasten the canister to the baseplate while also providing an outer gasket groove. An undue amount of forming sheet steel has often been necessary in many of the filters to form a U-shaped channel, with further forming of steel necessary to provide gasket retaining means. In aluminum type baseplates, further drawing of stress sensitive steel has often been necessary to provide torque transfer because aluminum type baseplates cannot be welded to sheet steel to provide for torque transfer. Excessive or uneven forming of steel, and particularly the forming of steel at stress sensitive areas, can reduce the strength of the filter. Furthermore, the forming of steel has often required more complex tooling and manufacture which increases manufacturing costs.